JP4233545B2 - Phosphorus removal equipment - Google Patents

Description

  The present invention relates to a method and apparatus for removing phosphorus from sewage, agricultural settlement drainage, domestic wastewater, human waste, industrial wastewater and the like.

  Since wastewater such as sewage, agricultural settlement wastewater, domestic wastewater, human waste, and industrial wastewater contains phosphorus, the water becomes eutrophication in lakes and closed waters where such wastewater flows. Has occurred. In the wastewater, there are non-soluble (also called suspended) phosphorus and soluble phosphorus. Among them, since soluble phosphorus cannot be removed by solid-liquid separation such as sedimentation in a sedimentation basin, a technique for solidifying or removing soluble phosphorus is required.

  Most of the soluble phosphorus in the wastewater exists as orthophosphate (orthophosphate) ions. As a method for solidifying this normal phosphate ion, four kinds of techniques, mainly an aggregation method, a biological dephosphorization method, an adsorption method, and a crystallization method, have been developed and put into practical use.

The agglomeration method is a technique for removing phosphate ions into an insoluble salt by adding an aggregating material. As the aggregating material, a salt of calcium, iron, aluminum or the like is used. The agglomeration method is the most practical technique because of its high removal efficiency and relatively easy operation.
However, there are problems such as high chemical costs and a large amount of sludge generation. For example, the amount of generated sludge is increased because other insoluble salts are simultaneously generated or mother liquor (water) is embraced when forming the aggregated salt. Furthermore, the sludge generated in this way is difficult to dehydrate. Therefore, it is difficult to reduce the amount of such sludge. Furthermore, in recent years, there is a demand for sludge reduction due to a shortage of final disposal sites. However, it is difficult to meet this requirement with the coagulation method.

The biological dephosphorization method is a wastewater treatment method that decomposes organic matter (BOD) by microbial sludge, such as activated sludge method, and is a method that removes phosphorus as sludge (microorganism) by incorporating phosphoric acid into microbial sludge. is there. The biological dephosphorization method has been introduced in recent years because it can be dealt with only by changing the design of the biological treatment tank (battery tank) in the conventional activated sludge treatment and the equipment cost is the lowest.
However, since the amount of inflowing phosphorus varies depending on the rainy season and season, when the inflow of phosphorus greatly fluctuates, it cannot cope with it and the processing may become unstable. In addition, in a treatment plant with a low inflow BOD, it may be necessary to add sludge or add organic substances. Therefore, it may be difficult to perform control so that the processing is always performed stably. Further, when sludge is decomposed in order to reduce the amount of sludge, phosphorus immobilized from the sludge is discharged, so it is difficult to reduce the sludge. Therefore, as with the above-described coagulation method, it cannot be a solution for reducing sludge.

The adsorption method is a method in which phosphoric acid is adsorbed on an adsorbent such as alumina or zirconia. The adsorption method is performed by passing the wastewater from which the SS (floating matter) is removed from the wastewater and the like through an adsorption tower filled with an adsorbent such as alumina, so that a large facility is not required. For this reason, it is a method suitable for a small-scale treatment plant.
However, an adsorbent having a weight of about 20 to 50 times the weight of phosphorus to be removed is required, and if the adsorbent adsorbing phosphorus is discarded as it is, the running cost becomes too high, and the adsorbent is regenerated and used. In order to do this, the problem is that infrastructure such as the distribution route and the recycling plant is necessary.

In the crystallization method, a supersaturated state of phosphorus is generated so that aggregated crystal nuclei are not formed, and a seed crystal is added to this saturated solution. By attaching phosphorus to the seed crystal and growing the crystal, phosphorus is precipitated and removed. As seed crystals, crystals such as calcium apatite, magnesium ammonium phosphate (MAP) and the like are used. The crystallization method is a technique that has advantages such as low chemical costs and low sludge generation.
However, it is difficult to control the maintenance of the supersaturated state of phosphorus in the treated water, and many processes such as a chemical injection process, a decarboxylation process, a pH adjustment process, a crystallization process, and a neutralization process are required. Problems such as the need for equipment / instrumentation equipment and the like, resulting in high initial costs, arise. Furthermore, since there are many operation processes as described above, it is difficult to control the equipment used in those processes.

For example, in order to solve the above-described problems in the crystallization method, it has been proposed to control the pH adjustment step using electrolysis or concentration by electrodialysis (see Patent Document 1 and Patent Document 2). ).
JP 2002-361258 A JP 2003-39081 A

  However, the technique described in Patent Document 1 still has the following problems: (1) Since an agglomeration reaction occurs together with a crystallization reaction of phosphate ions around the cathode, it settles in the cathode chamber. The amount of sludge increases and post-treatment such as dehydration becomes difficult (even if the pH is controlled by electrolysis, a high pH is generated near the cathode, and agglomerate precipitates are always generated); (2) Temporarily aggregate around the cathode Insoluble phosphate does not precipitate if there is not enough calcium ions in the wastewater even if the alkaline conditions are such that crystallization is unlikely to occur and crystallization is likely to occur. Instead, only other cationic hydroxides, including heavy metals, precipitate as insoluble materials; (3) If the supersaturation of phosphate in the cathode chamber is too high, it will be sparingly soluble in the walls and electrodes of the cell. Salt tends to precipitate, which hinders removal treatment.

  In the technique described in Patent Document 2, phosphoric acid is concentrated on the anode side by electrodialysis as a pretreatment for crystallization in order to increase the phosphorus removal rate in the crystallization reaction. However, the following problems occur: (i) Since the solution on the anode side is acidic, a large amount of alkali chemicals is required in order to make the solution on the anode side suitable for the crystallization reaction. (Ii) Even if alkaline water on the cathode side is added to the solution on the anode side by electrolysis, the pH of the solution on the anode side is only near neutral. For this reason, it is necessary to inject | pour alkali chemicals into the solution of an anode side.

  Then, an object of this invention is to provide the apparatus for removing phosphorus efficiently by simple operation.

A phosphorus removal apparatus according to a preferred embodiment of the present invention includes:
(1) An electrolytic cell comprising an anode and a cathode and containing at least phosphoric acid-containing waste water,
(2) Energizing means to energization between the anode and the cathode,
(3) Calcium ion supply means for supplying calcium ion to phosphoric acid-containing waste water, and
(4) Solid-liquid separation means for separating the phosphorus-containing crystals precipitated from the phosphoric acid-containing waste water and the waste water after the phosphorus-containing crystals are precipitated , the electrolytic cell includes an anode, and an aqueous solution containing calcium ions is provided. An anode chamber to be introduced; a cathode chamber provided with a cathode, into which phosphoric acid-containing wastewater is introduced; and a diaphragm disposed between the cathode chamber and the anode chamber, and being energized between the anode and the cathode To supply calcium ions to the phosphoric acid-containing wastewater . The phosphorus removing device preferably further includes means for introducing phosphoric acid-containing wastewater into the cathode chamber and means for supplying an aqueous solution containing calcium ions to the anode chamber. It is preferable that the phosphorus removing device further includes a calcium ion concentration adjusting means for adjusting the calcium ion concentration of the aqueous solution containing calcium ions. The phosphorus removal apparatus preferably includes a neutralizing means for neutralizing the anodic water generated in the anode chamber by adding to the waste water after separating the phosphorus-containing crystals, and after neutralizing by the neutralizing means It is preferable to further include a biological treatment tank for biologically treating the waste water.

The phosphorus removal apparatus according to another preferred embodiment of the present invention includes:
(1) An electrolytic cell comprising an anode and a cathode and containing at least phosphoric acid-containing waste water,
(2) energizing means for energizing between the anode and the cathode;
(3) Calcium ion supply means for supplying calcium ion to phosphoric acid-containing waste water, and
(4) Solid-liquid separation means for separating phosphorus-containing crystals precipitated from phosphoric acid-containing waste water and waste water after the phosphorus-containing crystals are precipitated is provided, and the electrolytic cell is provided between an anode, a cathode, and an anode and a cathode. at least one organic group of electrodes consisting of arranged diaphragm, in one of the at least one electrode group, the diaphragm is cylindrical, cylindrical cathodes are arranged inside the cylindrical diaphragm A cylindrical anode is disposed outside the cylindrical diaphragm . In the electrolytic cell, it is preferable that the seed crystal is movably held. At least one of the electrode groups preferably functions as a solid-liquid separation unit.

  It is preferable that the phosphorus removal apparatus further includes a supply unit that supplies phosphoric acid-containing wastewater to the electrolytic cell.

  In the phosphorus removal apparatus, it is more preferable to supply calcium ions to the phosphoric acid-containing waste water after the calcium ion supply means is discharged from the electrolytic cell.

  In the phosphorus removing apparatus, it is preferable that the solid-liquid separation means holds the seed crystal.

  More preferably, the phosphorus removal apparatus includes a crystal drawing means for discharging phosphorus-containing crystals.

  The phosphorus removing device preferably includes a measuring unit that measures at least one of a hydrogen ion concentration (pH), a calcium ion concentration, and a phosphoric acid concentration in the phosphoric acid-containing waste water.

  It is preferable that the phosphorus removing device further includes a circulation means for joining at least a part of the waste water discharged from the solid-liquid separation means to the phosphoric acid-containing waste water discharged from the electrolytic cell.

The present invention also provides:
(1) An electrolytic cell comprising an anode and a cathode and containing at least phosphoric acid-containing waste water,
(2) Energizing means to energization between the anode and the cathode,
(3) Calcium ion supply means for supplying calcium ions to the phosphoric acid-containing wastewater, and (4) Solid-liquid separation means for separating the phosphorus-containing crystals deposited from the phosphoric acid-containing wastewater and the wastewater after the phosphorus-containing crystals are deposited. The operation method of the phosphorus removal apparatus which comprises this. Using at least one of the energization means and the calcium supply means, the pH of the phosphoric acid-containing wastewater is adjusted to 8.5 to 10, and the calcium ion concentration is adjusted to 20 mg / L to 100 mg / L.

According to the present invention, since an appropriate supersaturated state of a salt composed of calcium and phosphorus can be formed in the phosphoric acid-containing waste water, the recovery rate of the salt composed of calcium and phosphorus by reaction crystallization can be improved. it can. That is, the soluble phosphorus component can be efficiently removed from the wastewater containing the phosphorus component.
Moreover, since it becomes possible to reduce that the aggregation reaction of a phosphorus component arises by formation of a suitable supersaturated state, the production amount of sludge can be reduced.
Moreover, since the phosphoric acid containing waste_water | drain accommodated in the electrolytic cell by electrolysis can be made alkaline, an alkaline chemical injection process can be reduced. Similarly, even when the electrolytic cell includes an anode chamber and a cathode chamber, the phosphoric acid-containing wastewater contained in the cathode chamber can be made into alkaline conditions by electrolysis, which can reduce the alkaline chemical injection process. it can. Furthermore, the solution contained in the anode chamber becomes acidic by electrolysis. By using this acidic solution, the step of preparing the acidic solution necessary for neutralizing the phosphoric acid-containing wastewater after separating the phosphorus-containing crystals can be reduced.

Hereinafter, the present invention will be described with reference to the drawings.
FIG. 1 schematically shows a wastewater treatment facility equipped with the phosphorus removal apparatus of the present invention. In addition, although the structure changes with kinds of facilities, such as a public sewage treatment facility, an agricultural settlement drainage facility, and a septic tank, the basic structure is as having shown in FIG.

The wastewater treatment facility 10 includes a first sedimentation tank 11, a biological treatment tank 12, a second sedimentation tank 13, a sludge treatment tank 14, and a phosphorus removal device 15.
First, sewage such as drainage and sewage enters the first settling basin 11. In the 1st sedimentation basin 11, some insoluble organic substances, inorganic substances, etc. contained in sewage are settled and separated. The supernatant produced in the first sedimentation basin 11 is sent to the biological treatment tank 12.

  In the biological treatment tank 12, organic matter (BOD) or the like is taken up by microorganisms (sludge). Part of the incorporated BOD is reduced by being decomposed into carbon dioxide and water by microorganisms. Since the remaining BOD is used for the growth of microorganisms, the amount of sludge increases.

  Subsequently, the biologically treated water containing the sludge discharged from the biological treatment tank 12 is transferred to the second sedimentation tank 13. In the 2nd sedimentation basin 13, solid content, such as sludge contained in biologically treated water, is settled and separated.

At least a part of the solid content settled and separated in the second sedimentation basin 13 is extracted as return sludge and returned to the biological treatment tank 12 by the return means 16. Moreover, the remaining solid content settled and separated in the second settling basin 13 is extracted as excess sludge. This excess sludge is introduced into the sludge treatment tank 14. These excess sludges have a water content of approximately 98% by weight or more. In the sludge treatment tank 14, the water content of the sludge is set to approximately 60 to 80% by weight by solid-liquid separation processes such as concentration, dehydration, and digestion. The separated solid content is treated as disposal sludge. The sludge treated water separated in the sludge treatment tank 14 is transferred to the biological treatment tank 12 by the sludge treated water transfer means 17. This sludge treated water contains phosphorus of a predetermined concentration discharged from the sludge.

As described above, in the biological treatment tank 12, a part of the BOD taken into the microorganism is decomposed into carbon dioxide gas and water, and the rest is used as a carbon source for the growth of the microorganism. When the microorganism in the biological treatment tank 12 takes in BOD, it takes in soluble orthophosphoric acid (PO ₄ ³⁻ ) among the phosphorus present in the biological treatment tank 12 as a nutrient salt. The phosphorus that has not been taken up by the microorganisms is introduced into the second sedimentation basin 13. However, soluble phosphorus such as orthophosphoric acid is not separated in the second sedimentation basin.

Thus, the phosphoric acid containing waste water discharged | emitted from the 2nd sedimentation basin 13 contains phosphorus of predetermined concentration. For example, phosphorus contained in treated water has many forms such as orthophosphoric acid, linear polyphosphoric acid (such as pyrophosphoric acid and tripolyphosphoric acid), cyclic metaphosphoric acid, and organic phosphorus. Of these, orthophosphoric acid accounts for the majority. In addition, orthophosphoric acid is present as PO ₄ ³⁻ , HPO ₄ ²⁻ , and H ₂ PO ^{4− in the} wastewater, and the abundance ratio varies depending on the pH of the phosphoric acid-containing wastewater. It is this orthophosphoric acid to be removed in the present invention.

  In the wastewater treatment facility shown in FIG. 1, a phosphorus removal device 15 is installed after the second sedimentation tank 13. The phosphorus component contained in the phosphoric acid-containing wastewater discharged from the second sedimentation basin 13 is removed by the phosphorus removal device 15.

Next, the case where the phosphorus removal apparatus of the present invention is applied to a wastewater treatment facility having a configuration different from the wastewater treatment facility shown in FIG. 1 will be described with reference to FIG. In addition, the same number is attached | subjected to the component similar to FIG.
The wastewater treatment facility 20 in FIG. 2 includes a first sedimentation tank 11, a biological treatment tank 12, a second sedimentation tank 13, a sludge solubilization tank 21, a solid separation tank 22, and a phosphorus removal device 15.

The process from the 1st sedimentation basin 11 to the 2nd sedimentation basin 13 is the same as that of the above.
At least a part of the solid content settled and separated in the second settling basin 13 is extracted as return sludge and returned to the biological treatment tank 12 by the transfer means 16.

  The remaining solid content settled and separated in the second sedimentation tank 13 is extracted as excess sludge and introduced into the sludge solubilization tank 21. These sludges have a water content of about 98% by weight or more. In the sludge solubilization tank 21, the surplus sludge is solubilized by mill crushing, ozone treatment, ultrasonic treatment, or the like. By this solubilization treatment, surplus sludge can be biologically treated again, so that the amount of sludge discharged outside the system can be reduced.

  As described above, the microorganism (sludge) in the biological treatment tank 12 takes in soluble orthophosphoric acid as a nutrient salt among phosphorus existing in the biological treatment tank 12 when taking in BOD. When such sludge is solubilized in the sludge solubilization tank 21, orthophosphoric acid taken in as nutrients is discharged again. Therefore, the solubilization process liquid produced by solubilization process will contain a high concentration phosphoric acid, and the density | concentration will be 10 mg / L-about 50 mg / L.

  The solubilization processing liquid is transferred to the solid separation tank 22. The solid content is separated in the solid separation tank 22. The separated solid content is processed outside the system. The treatment liquid from which the solid content has been separated contains a high concentration of phosphate ions as described above. In order to remove the phosphoric acid component, the treatment liquid from which the solid content has been separated is introduced into the phosphorus removal device 15 by the first treatment liquid transfer means 23.

The treatment liquid from which the phosphorus component has been removed by the phosphorus removal device is transferred to the biological treatment tank 12 by the second treatment liquid transfer means 24 and biologically processed. Alternatively, the treatment liquid from which the phosphorus component has been removed can be discharged out of the system as it is.
As described above, in the wastewater treatment facility, the phosphoric acid component is removed from the phosphoric acid-containing wastewater by the phosphorus removal device. Hereinafter, a phosphorus removal apparatus will be described.

The phosphorus removal apparatus of the present invention comprises:
(1) An electrolytic cell comprising an anode and a cathode and containing at least phosphoric acid-containing waste water,
(2) Energizing means to energization between the anode and the cathode,
(3) Calcium ion supply means for supplying calcium ion to phosphoric acid-containing waste water, and
(4) A solid-liquid separation means for separating the phosphorus-containing crystals precipitated from the phosphoric acid-containing wastewater and the wastewater after the phosphorus-containing crystals are precipitated is provided.
In the present invention, the solid-liquid separation means may be provided separately from the electrolytic cell, or may be provided in the electrolytic cell.
Hereinafter, preferred embodiments of the present invention will be described.

Embodiment 1
FIG. 3 schematically shows an apparatus for removing phosphorus according to an embodiment of the present invention. In the present embodiment, the solid-liquid separation means is provided separately from the electrolytic cell.
3 includes an electrolytic cell 31 and a reaction crystallization tank 39 which is a solid-liquid separation means.
The electrolytic cell 31 includes an anode chamber 32, a cathode chamber 33, and a diaphragm 34 disposed between the anode chamber 32 and the cathode chamber 33. The anode chamber 32 includes an anode 35, and the cathode chamber 33 includes a cathode 36. Further, the cathode chamber 33 includes a stirring means 37. In addition, the phosphorus removing device 15 includes an energizing means 38 for energizing between the anode 35 and the cathode 36. The reaction crystallization tank 39 is in communication with the cathode chamber 33, and calcium hydroxyapatite, which is a phosphorus-containing crystal, is deposited in the reaction crystallization tank 39. In addition, calcium hydroxyapatite can be represented by, for example, Ca ₁₀ (PO ₄ ) ₆ (OH) ₂ .

  The phosphoric acid-containing waste water is introduced into the cathode chamber 33 of the electrolytic cell 31. An aqueous solution containing calcium ions (hereinafter also referred to as anode water) is introduced into the anode chamber 32. As such an aqueous solution containing calcium ions, calcium chloride, calcium hydroxide, gypsum, byproduct gypsum or the like dissolved in water, hard water containing calcium ions, or the like can be used.

After the phosphoric acid-containing wastewater is accommodated in the cathode chamber and the anode water is accommodated in the anode chamber, the energization means 38 is used to energize between the anode 35 and the cathode 36. Thereby, phosphoric acid containing waste water and anode water are electrolyzed. Due to this electrolysis, the cathode 36 has the following formula:
2H ₂ O + 2e ⁻ → H ₂ + 2OH ⁻ (1)
The reaction shown in FIG. 4 occurs, and hydroxide ions (OH ⁻ ) are generated. This hydroxide ion makes the phosphoric acid-containing wastewater alkaline.

When a solution in which calcium chloride is dissolved as anode water is accommodated in the anode chamber, the following formula is applied to the anode:
2H ₂ O → O ₂ + 4H ⁺ + 4e ⁻ (2)
2Cl ⁻ + 2e ⁻ → Cl ₂ (3)
Cl ₂ + 2H ₂ O → HCl + HClO (4)
The reaction shown in FIG. 4 occurs, and hydrogen ions (H ⁺ ) are generated. This hydrogen ion makes the anode water acidic.

In addition, it is preferable to use the titanium electrode plated with platinum so that a titanium ion may not elute. The electrolysis conditions are preferably a voltage of 5 to 50 V and a current of ² to 600 A / m ² per electrode surface area.

  During electrolysis, ions move between the phosphoric acid-containing waste water and the anode water due to the potential difference between the anode and the cathode. In the present invention, a diaphragm is disposed between the anode chamber 32 and the cathode chamber 33. As this diaphragm, it is preferable to use a cation exchange membrane. By using a cation exchange membrane, calcium ions and hydrogen ions, which are cation species, can move from the anode water to the phosphoric acid-containing waste water. On the other hand, due to the Donan exclusion effect of the cation exchange membrane, the anion species does not move from the phosphoric acid-containing waste water to the anode water. Therefore, the phosphate ion species in the phosphoric acid-containing wastewater is retained in the phosphoric acid-containing wastewater, and calcium ions in the anodic water are supplied to the phosphoric acid-containing wastewater according to the potential difference generated by electrolysis.

  Since the movement of ionic species occurs through the diaphragm as described above, the pH of the phosphoric acid-containing wastewater can be adjusted by adjusting the voltage and current applied between the anode and the cathode with the energizing means. . In addition, the voltage and current applied between the anode and the cathode are adjusted by the adjusting means, and the calcium ion concentration of the phosphoric acid-containing waste water can be adjusted by adjusting the calcium ion concentration of the anode water. . That is, by setting it as the above structures, it becomes possible to supply calcium ion to phosphoric acid containing waste water, adjusting the pH of phosphoric acid containing waste water.

  In this case, the pH of the phosphoric acid-containing wastewater is preferably 8.5 or more and 10 or less. If the pH of the phosphoric acid-containing wastewater is smaller than 8.5, the solubility of calcium hydroxyapatite is increased, so that even when calcium ions are added, the supersaturation degree of calcium hydroxyapatite is difficult to increase. Accordingly, calcium hydroxyapatite is hardly crystallized. On the other hand, if the pH is higher than 10, the supersaturation degree of calcium phosphate increases even at the level of calcium ion concentration normally contained in sewage, waste water, clean water and the like. For this reason, calcium phosphate tends to aggregate and precipitate. In addition, calcium hydroxide may be generated from calcium ions and hydroxide ions, and this calcium hydroxide may precipitate.

  The calcium ion concentration of the phosphoric acid-containing wastewater is preferably 20 mg / L or more and 100 mg / L or less. If the calcium ion concentration is less than 20 mg / L, the supersaturation degree of calcium hydroxyapatite may not be increased. On the other hand, if the calcium ion concentration is higher than 100 mg / L, the calcium content becomes excessive, and precipitation of calcium salt may cause scale and precipitation sludge.

  The concentration of calcium ions contained in the anode water is preferably 10 to 300 mg / L. When the calcium ion concentration is less than 10 mg / L, there may be a case where sufficient calcium ions cannot be supplied to the phosphoric acid-containing waste water in the cathode chamber even when the current is supplied between the anode and the cathode by the current supply means. On the other hand, when the calcium ion concentration is higher than 300 mg / L, the supply of calcium ions to the phosphoric acid-containing waste water may be excessive. For this reason, the scale which consists of calcium salts precipitates, and the inside of a tank and an electrode may be contaminated.

During electrolysis, the pH rises in the vicinity of the cathode where hydroxide ions (OH ⁻ ) are generated in the phosphoric acid-containing wastewater. In addition, calcium ions move from the anode water to the phosphoric acid-containing waste water. For this reason, in phosphoric acid-containing wastewater, the insoluble salt formed from phosphate ions, calcium ions, and hydroxide ions may become unstable beyond the supersaturated state, resulting in the formation of aggregated nuclei. There is. Accordingly, it is preferable to agitate the phosphoric acid-containing wastewater in the cathode chamber during electrolysis to homogenize the distribution of ionic species in the phosphoric acid-containing wastewater.

  As shown in FIG. 3, the phosphoric acid-containing wastewater can be stirred by rotating the phosphoric acid-containing wastewater by rotating the stirring means 37 installed in the cathode chamber. For example, as the agitation means, small agitation blades such as a turbine, a paddle, an inclined paddle, a ribbon blade, an anchor blade or the like can be used alone or in combination. In addition, Max Blend (manufactured by Sumitomo Heavy Industries, Ltd.), Full Zone (manufactured by Shinko Pantech Co., Ltd.), Sun Meller (manufactured by Mitsubishi Heavy Industries, Ltd.), Supermix (manufactured by Satake Chemical Machinery Co., Ltd.), Large special blades sold under a trade name such as Hi-F mixer (manufactured by Soken Chemical Co., Ltd.) can also be used as the stirring means. Alternatively, the phosphoric acid-containing wastewater can be agitated by circulating and flowing the phosphoric acid-containing wastewater using a pump installed outside the cathode chamber.

  As described above, the pH and calcium ion concentration of the phosphoric acid-containing wastewater are adjusted so that the calcium hydroxyapatite composed of orthophosphate ions, calcium ions, and hydroxide ions becomes supersaturated in the phosphoric acid-containing wastewater. Adjust. At this time, it is confirmed that no precipitate is deposited in the phosphoric acid-containing waste water, and the electric power for energization and the calcium ion concentration of the anode water are increased within a range in which the precipitate is not deposited. Thereby, the phosphoric acid containing waste water can be made into the state with high supersaturation degree of calcium hydroxyapatite, ie, the state which calcium hydroxyapatite is easy to crystallize, avoiding the aggregation of the phosphate in a cathode chamber.

In addition, when the fluctuation of the concentration of the phosphoric acid component in the phosphoric acid-containing wastewater is small, once the pH of the phosphoric acid-containing wastewater and the calcium ion concentration are controlled by controlling the power of the energizing means and the calcium ion concentration of the anode water Adjust. In this case, a long period of time,必short not to adjust the calcium ion concentration of power and anode water energizing means.

  When the concentration of the phosphoric acid component in the phosphoric acid-containing wastewater varies greatly, the power for energization and the calcium ion concentration of the anode water are adjusted again when precipitation occurs in the phosphoric acid-containing wastewater.

The supersaturated solution thus formed in the cathode chamber is transferred to the reaction crystallization tank 39 which is a solid-liquid separation means. The reaction crystallization tank 39 preferably holds seed crystals (not shown) such as calcium apatite, phosphate ore, and bone charcoal. When the phosphoric acid-containing wastewater that is supersaturated with calcium hydroxyapatite comes into contact with the seed crystal in the reaction crystallization tank, calcium hydroxyapatite is deposited on the surface of the seed crystal, and the seed crystal is enlarged. After the calcium hydroxyapatite is precipitated, the seed crystal remains in the reaction crystallization tank, and the waste water after the calcium hydroxyapatite is precipitated is discharged from the reaction crystallization tank. In the waste water after the calcium hydroxyapatite is deposited, the concentrations of phosphate ions, calcium ions, and hydroxide ions decrease.
In this way, the phosphorus component can be removed from the phosphoric acid-containing wastewater by separating calcium hydroxyapatite and the wastewater after the precipitation thereof.
The reaction crystallization tank may be in the form of a fixed bed, a fluidized bed, or a complete mixed bed. Moreover, the particle diameter of the seed crystal is preferably 0.1 mm or more and 20 mm or less.

  The residence time of the phosphoric acid-containing wastewater in the reaction crystallization tank becomes shorter in proportion to the degree of supersaturation. The residence time of the phosphoric acid containing waste water in a reaction crystallization tank becomes short, so that supersaturation degree is enlarged by the electricity supply etc. in an electrolytic tank. Furthermore, since the residence time can be shortened, the volume of the reaction crystallization tank can be reduced. Therefore, in the formation of the supersaturated state, increasing the pH and the calcium ion concentration as much as possible within a range where precipitation does not occur contributes to acceleration of the reaction crystallization or downsizing of the phosphorus removal apparatus.

  The solubility product shows a constant value if the temperature is constant. Therefore, if the calcium ion concentration and pH in the phosphoric acid-containing wastewater are determined, the concentration of the phosphorus component contained in the phosphoric acid-containing wastewater is also determined from the solubility product. Therefore, by adjusting the calcium ion concentration and the pH within a predetermined range, the phosphoric acid concentration of the waste water after crystallization can be made to fall within a substantially constant range.

  In the phosphorus removing apparatus, the cathode chamber wall and the like are preferably made of a transparent member such as glass or acrylic resin. As a result, it is possible to visually confirm whether or not a precipitate is deposited in the phosphoric acid-containing wastewater in the cathode chamber.

  The phosphorus removal apparatus may include a crystal drawing means for discharging the enlarged seed crystal (that is, phosphorus-containing crystal) from the reaction crystallization tank. This crystal drawing means can be constructed from those known in the art.

Embodiment 2
A case where the phosphorus removing device has means for measuring the water quality of the phosphoric acid-containing waste water will be described with reference to FIG. In FIG. 4, the same components as those in FIG.
The phosphorus removal apparatus 40 of FIG. 4 further includes a measuring means 41 that measures the water quality of the phosphoric acid-containing wastewater in the cathode chamber in addition to the phosphorus removal apparatus of the first embodiment. In FIG. 4, the stirring means and the reaction crystallization tank are not shown. Here, the water quality of the phosphoric acid-containing wastewater refers to the concentration, pH, and calcium ion concentration of the phosphoric acid component.

The measuring means 41 that measures the water quality of the phosphoric acid-containing wastewater preferably measures at least one of pH, calcium ion concentration, and phosphoric acid concentration.
For example, when the measuring means 41 measures pH, the energizing means can be controlled based on the measurement result to keep the pH of the phosphoric acid-containing waste water constant. In this case, it is preferable to have pH control means for controlling the energization means so that the pH of the phosphoric acid-containing wastewater is maintained within a predetermined range based on the measurement value from the measurement means.

In the case of phosphoric acid-containing wastewater with stable phosphoric acid concentration and alkalinity, as described above, the pH of the phosphoric acid-containing wastewater is kept constant. What is necessary is just to control the calcium ion concentration.
However, in the case of wastewater with unstable phosphoric acid concentration or alkalinity, the pH of the phosphoric acid-containing wastewater is measured by the measuring means 41 and the current-carrying means is controlled so that the phosphoric acid-containing wastewater in the cathode chamber cannot be precipitated. In addition, the pH can be adjusted to be constant. If precipitation occurs in the phosphoric acid-containing wastewater even when the pH is adjusted, the calcium ion concentration of the anode water is adjusted so that precipitation does not occur in the phosphoric acid-containing wastewater.

In this way, while avoiding phosphoric acid aggregation in the phosphoric acid-containing wastewater, the phosphoric acid-containing wastewater can be brought into a state where the supersaturation degree of calcium hydroxyapatite is high, that is, a state in which crystallization is easier.
In the present embodiment, since the pH of the phosphoric acid-containing wastewater can be measured and controlled as described above, the phosphoric acid-containing wastewater is continuously passed through the cathode chamber for treatment. It becomes possible to continue stably.

  In the cathode chamber, as described above, the pH of the phosphoric acid-containing wastewater is preferably adjusted to 8.5 or more and 10 or less.

  Moreover, the measuring means 41 may measure both the pH and the calcium ion concentration of the phosphoric acid-containing waste water. There is a range in the phosphoric acid concentration contained in the phosphoric acid-containing wastewater. For this reason, the measurement means measures the pH and calcium ion concentration of the phosphoric acid-containing wastewater, and based on the measurement results, the electric power for energization is adjusted so that the pH and calcium ion concentration of the phosphoric acid-containing wastewater are within a predetermined range. It is preferable to adjust the calcium ion concentration of the anode water. Similarly to the above, the pH of the phosphoric acid-containing wastewater in the cathode chamber is preferably 8.5 or more and 10 or less, and the calcium ion concentration is preferably 20 mg / L or more and 100 mg / L or less.

  The measurement and control of pH and calcium ion concentration may be about once a day. When the water quality of the phosphoric acid-containing wastewater is stable, the phosphorus removal process can be performed stably even at a measurement interval such as once a month to once a year.

The pH of the phosphoric acid-containing wastewater can be measured, for example, by introducing a pH sensor in-line into the phosphoric acid-containing wastewater.
The calcium ion concentration can be measured according to the JIS K0102 factory drainage test method. In this case, the calcium ion concentration is quantified by any one of chelate titration, flame atomic absorption, or ICP emission spectroscopic analysis. For example, the calcium ion concentration can be measured using an in-line measurement system that automatically samples a portion of the phosphoric acid-containing wastewater with a pump and automatically performs chelate titration. Moreover, a calcium ion concentration can also be measured using a calcium ion meter provided with a calcium ion electrode.

  Moreover, also in this embodiment, it is preferable that the wall of a cathode chamber, etc. are comprised from a transparent member so that the production | generation of the precipitation in phosphoric acid containing waste water can be confirmed visually.

  Further, the control of the pH and / or the control of the calcium ion concentration of the anodic water is performed by adjusting the power of the energizing means based on the measurement result of the measuring means or the calcium described in the third embodiment below. It may be performed by ion concentration adjusting means.

  Further, the measuring means 41 may further measure the phosphoric acid concentration. Thereby, according to the phosphoric acid concentration contained in phosphoric acid containing wastewater, it becomes possible to adjust pH and calcium ion concentration of phosphoric acid containing wastewater. Also in this case, as described above, it is preferable to provide a control unit that controls the energization unit based on the output from the measurement unit 41.

Embodiment 3
A case where the phosphorus removing device includes calcium ion concentration adjusting means for adjusting the calcium ion concentration of the anode water will be described with reference to FIG. In FIG. 5, the same components as those in FIG.
The phosphorus removal apparatus 50 of FIG. 5 includes a calcium ion concentration adjusting means for adjusting the calcium ion concentration of the anode water in the anode chamber 32 in addition to the phosphorus removal apparatus of the first embodiment. In FIG. 5, the stirring means and the reaction crystallization tank are not shown.

  The calcium ion concentration adjusting means shown in FIG. 5 includes a storage tank 51 for storing a calcium ion-containing aqueous solution and a pump 52 for circulating the calcium ion-containing solution. Here, as the calcium ion-containing solution, a solution having a calcium ion concentration higher than the calcium ion concentration of the anode water can be used.

For example, when calcium ions contained in the anode water move to the phosphoric acid-containing waste water and the calcium ion concentration in the anode water decreases, the calcium ion-containing solution stored in the storage tank 51 is circulated to the anode chamber 32 by the pump 52. It is possible to increase the calcium ion concentration of anode water.
In addition, by filling the storage tank 51 with calcium ion exchange resin and passing the anode water, the hydrogen ions in the anode water can be exchanged for calcium ions and supplied to the anode water.

5 shows, calcium ion concentration adjusting means, shows a case that have a single storage tank and one pump. Besides configuration shown in FIG. 5, for example, a storage tank and pump, respectively are two by two is prepared, on one, the calcium ion concentration than the anode water to accommodate the high solution. On the other hand, a solution having a calcium ion concentration lower than that of the anode water is accommodated. Thereby, the density | concentration of the calcium ion in a phosphoric acid containing waste water can be raised so that a crystal | crystallization may not arise in the phosphoric acid containing waste water of a cathode chamber. On the other hand, when crystals are generated in the phosphoric acid-containing wastewater, the anode water is circulated in a storage tank containing a solution having a calcium ion concentration lower than that of the anode water, thereby reducing the concentration of calcium ions in the anode water. Thereby, it becomes possible to adjust the calcium ion concentration in the phosphoric acid-containing waste water. In this case as well, as described above, the calcium ion concentration of the phosphoric acid-containing waste water is preferably adjusted to 20 mg / L to 100 mg / L.

  Moreover, when it has a measuring means shown in Embodiment 2, based on the measured value of the calcium ion concentration of the phosphoric acid containing wastewater measured by the measuring means, so that the calcium ion of phosphoric acid containing wastewater becomes a predetermined range. In addition, the calcium ion concentration adjusting means may adjust the calcium ion concentration of the anode water.

  Alternatively, the calcium ion concentration of the phosphoric acid-containing wastewater may be adjusted by directly supplying the calcium ion-containing solution to the phosphoric acid-containing wastewater in the cathode chamber. This supply can be performed by, for example, calcium ion supply means (not shown). The calcium ion supply means can be composed of, for example, a storage tank that stores the calcium ion-containing solution and a transfer means for transferring the calcium ion-containing solution from the storage tank to the cathode chamber. At this time, the anode water accommodated in the anode chamber may or may not contain calcium ions.

In many cases, the phosphoric acid-containing wastewater in the cathode chamber contains a predetermined concentration of calcium ions in advance. For this reason, the supersaturation degree of calcium hydroxyapatite can be controlled only by adjusting the pH of the phosphoric acid-containing waste water in the cathode chamber.
In this case, since only the pH of the phosphoric acid-containing wastewater has to be adjusted by controlling the power during electrolysis, control of the power during electrolysis is relatively easy.

Embodiment 4
The case where the phosphorus removing device has a neutralization tank for neutralizing the waste water after separating the phosphorus-containing crystals will be described with reference to FIG. In FIG. 6, the same components as those in FIG.
In addition to the phosphorus removal apparatus of the first embodiment, the phosphorus removal apparatus 60 of FIG. 6 is a neutralization tank 61 for neutralizing wastewater from which phosphorus-containing crystals are separated and discharged from the reaction crystallization tank. Is further provided. In the present embodiment, the neutralization tank 61 communicates with the reaction crystallization tank 39. In FIG. 6, the stirring means is not shown.

  The wastewater discharged from the reaction crystallization tank is discharged into, for example, a sewer. In this case, the pH of the waste water discharged from the reaction crystallization tank is preferably 5.8 or more and 8.6 or less which is the discharge standard. However, the pH of the drainage may not be 8.6 or less. In such a case, it is necessary to neutralize the waste water.

In this embodiment, neutralization of the waste water after reaction crystallization can be performed as follows.
The waste water discharged from the reaction crystallization tank is introduced into the neutralization tank 61, and the anode water in the anode chamber is introduced into the neutralization tank 61. Since this anodized water is acidic, the pH of the drainage can be lowered to 5.8 or more and 8.6 or less. Here, the acidic anode water is transferred from the anode chamber 32 to the neutralization tank 61 by the transfer means 62.

  Thus, even when the pH of the wastewater discharged from the reaction crystallization tank is high, the wastewater can be neutralized without adding a neutralizing agent from the outside by using acidic anode water.

Further, when an aqueous calcium chloride solution is used as the anode water, chlorine and hypochlorous acid are generated by electrolysis. By using such anodized water, the phosphoric acid-containing waste water can be disinfected and deodorized.
The neutralized waste water may be discharged to the outside as it is, or may be transferred to a biological treatment tank and treated there again.

Embodiment 5
The phosphorus removing device includes a circulation means for mixing a part of the waste water discharged from the reaction crystallization tank with the phosphoric acid-containing waste water discharged from the cathode chamber in order to more efficiently remove the phosphorus component. The case will be described with reference to FIG. In FIG. 7, the same components as those in FIG. Also in FIG. 7, the stirring means is not shown.
In addition to the phosphorus removal device 60 shown in the fifth embodiment, the phosphorus removal device 70 of FIG. 7 is configured to remove at least a part of the wastewater discharged from the reaction crystallization tank 39 from the cathode chamber 33. A circulation means 71 for mixing with the acid-containing waste water is provided.

At least a part of the wastewater discharged from the reaction crystallization tank 39 is mixed with the phosphoric acid-containing wastewater discharged from the cathode chamber 33 by the circulation means 71 and introduced into the reaction crystallization tank 39 again. Thereby, the opportunity for the calcium apatite constituent in the waste water discharged from the reaction crystallization tank to come into contact with the seed crystal is increased, and the rate of reaction crystallization is improved. Therefore, the phosphorus removal efficiency in the phosphoric acid-containing wastewater can be improved.
Furthermore, even when the pH of the waste water discharged from the reaction crystallization tank 39 is high, it can be neutralized in the neutralization tank 61 using the anode water transferred by the transfer means 62.

Embodiment 6
A case where the phosphorus removal apparatus does not include a reaction crystallization tank and a seed crystal is introduced into the cathode chamber will be described with reference to FIG. In FIG. 8, the same components as those in FIG. Also in FIG. 8, the stirring means is not shown.
Unlike the first embodiment, the phosphorus removal apparatus 80 of FIG. 8 does not have a reaction crystallization tank, and a seed crystal 81 is introduced into the cathode chamber 33. Thereby, in the cathode chamber 33, formation of a supersaturated state and crystallization reaction can be performed simultaneously.

  In this case, it is necessary to perform regular maintenance and to prevent the scale from adhering to the cathode 36, the cation exchange membrane 34, the wall surface of the cathode chamber 33, etc. by using a backwashing means (not shown). Moreover, it is preferable to provide a means for pulling out the enlarged seed crystal (not shown) and a means for separating the enlarged seed crystal (not shown).

Embodiment 7
FIG. 9 shows a phosphorus removing apparatus according to still another embodiment of the present invention. In FIG. 9, the same components as those in FIG.
The phosphorus removal apparatus 90 of FIG. 9 is different from the phosphorus removal apparatus of FIG. 3 in that no diaphragm is disposed in the electrolytic cell. Moreover, the phosphorus removal apparatus of FIG. 9 includes calcium ion supply means 91 for supplying calcium ions to the phosphoric acid-containing wastewater that is energized in the electrolytic cell.

As described above, when removing the soluble phosphorus component as calcium hydroxyapatite, it is necessary to adjust the pH of the phosphoric acid-containing wastewater and the concentration of calcium ions contained in the phosphoric acid-containing wastewater. In the present embodiment, the pH of the phosphoric acid-containing wastewater is adjusted, and then the calcium ion concentration is adjusted.

  First, phosphoric acid-containing wastewater containing a soluble phosphorus component is introduced into the electrolytic cell 31. In the electrolytic cell 31, a stirring means 37, and an anode 35 and a cathode 36 are arranged without a diaphragm.

  Next, the pH of the phosphoric acid-containing waste water is adjusted to a pH suitable for the crystallization reaction of calcium hydroxyapatite. In the same manner as described above, the pH is adjusted by energizing between the anode 35 and the cathode 36 using the energizing means 38 and electrolyzing the phosphoric acid-containing waste water.

By this electrolysis, hydroxide ions (OH ⁻ ) are generated at the cathode 36 as shown in the above formula (1). This hydroxide ion makes the phosphoric acid-containing wastewater near the cathode alkaline.
When the phosphoric acid-containing wastewater further contains chloride ions, hydrogen ions (H ⁺ ) are generated as shown in the above formulas (2) to (4).

In this embodiment, there is no diaphragm between the anode and the cathode installed in the electrolytic cell. Therefore, at this time, in the phosphoric acid-containing wastewater in the electrolytic cell, the following formula:
H ⁺ + OH ⁻ → H ₂ O (5)
The neutralization reaction shown in FIG. However, as a result of the experiment, it is not completely neutral, and the pH of the phosphoric acid-containing wastewater is in the range of 8-9. This pH range is suitable for the crystallization reaction of calcium hydroxyapatite. Furthermore, in this embodiment, it is preferable to adjust the pH of the phosphoric acid-containing waste water to a range of 8.5 or more and 9 or less by adjusting electrolysis conditions and the like. Thereby, the supersaturation degree of calcium hydroxyapatite can be further increased.

Also in the present embodiment, as in the first embodiment, it is preferable to use a platinum-plated titanium electrode so that titanium ions are not eluted. Further, as the electrolysis conditions, the voltage is preferably 5 to 50 V, and the current is preferably ² to 600 A / m ² per electrode surface area.

  In the conventional alkaline chemical injection, the pH of the portion to which the alkaline chemical is added is locally increased, and the supersaturation degree of the salt composed of phosphorus and calcium is increased, which may cause aggregation. On the other hand, in the present invention, since hydroxide ions are supplied from the entire electrode surface by performing electrolysis in the phosphoric acid-containing wastewater, uniformity when the hydroxide ions are supplied to the phosphoric acid-containing wastewater. Is improved as compared with the conventional case.

In this embodiment as well, as in the first embodiment, it is preferable to stir the phosphoric acid-containing wastewater in order to homogenize the distribution of ionic species in the phosphoric acid-containing wastewater contained in the electrolytic cell. . In addition, the same stirring means as that in the first embodiment can be used.
Furthermore, by stirring the phosphoric acid-containing wastewater, the neutralization reaction represented by the above formula (5) can be quickly performed.

Next, the pH is adjusted, and calcium ions are supplied to the phosphoric acid-containing wastewater discharged from the electrolytic cell. This supply of calcium ions is performed by the calcium ion supply means 91. Supply of calcium ions may be performed by adding an aqueous solution containing calcium ions to a phosphate-containing wastewater whose pH is adjusted, or a salt that dissolves in water to produce calcium ions is added to the phosphate-containing wastewater. It may be done by doing.
In addition, the supply means 91 can be comprised from the tank which accommodates the aqueous solution etc. which contain calcium ion, the transfer means etc. which transfer the aqueous solution etc. As the transfer means, for example, a valve, a pump, or a combination of a valve and a pump can be used.
As the aqueous solution containing calcium ions, the same solution as in the first embodiment can be used. Calcium chloride, calcium hydroxide, gypsum, byproduct gypsum and the like may be added directly to the phosphoric acid-containing waste water.
In addition, it is preferable that the calcium ion concentration of the phosphoric acid containing waste_water | drain with which the calcium ion was supplied by the supply means 91 is 20 mg / L-100 mg / L similarly to the said Embodiment 1. FIG.

When the calcium ion concentration and the hydroxide ion concentration of the phosphoric acid-containing wastewater are adjusted, a supersaturated state of calcium hydroxyapatite may be formed at the same time as supersaturation of calcium carbonate may be formed. Therefore, there is a possibility that calcium carbonate precipitates due to an increase in the calcium ion concentration in the phosphoric acid-containing waste water.
When precipitation of calcium carbonate occurs, calcium ions, which are raw materials for calcium hydroxyapatite, decrease, and there is a possibility that a phosphorus crystallization reaction that produces calcium hydroxyapatite does not occur. Furthermore, this calcium carbonate becomes a causative substance of sludge and scale.
Therefore, it is preferable to make the supersaturation degree of calcium hydroxyapatite as high as possible and make the supersaturation degree of calcium carbonate as low as possible.

FIG. 10 shows the solubility curve of calcium carbonate. Here, the vertical axis represents the logarithm of the calcium ion concentration (C _ca ) in the solution, and the horizontal axis represents the pH of the solution.
The solubility curve of calcium carbonate varies depending on the alkalinity of the solution. For example, even when the pH is the same, when the alkalinity of the solution is small, calcium carbonate precipitation does not occur unless the calcium ion concentration (C _ca ) in the solution is increased. The alkalinity is related to the amount of bicarbonate ion, carbonate ion, hydroxide, etc. present in the solution, and is the amount of hydrogen ion (acid amount) required to bring the solution to a predetermined pH. To express.

  In FIG. 10, it is assumed that the pH and calcium ion concentration required to form a supersaturated state of calcium hydroxyapatite are point b. Further, it is assumed that the phosphoric acid-containing wastewater has a pH and a calcium ion concentration indicated by point a.

  In the case of point a, calcium carbonate is rarely precipitated regardless of the degree of alkalinity. However, in the case of point b required for supersaturation formation of calcium hydroxyapatite, it is preferable to reduce the alkalinity because the calcium ion concentration exceeds the solubility curve of calcium carbonate. For example, the alkalinity can be reduced by using a decarboxylation means such as a means for blowing air in an acid state.

In the present embodiment, as described above, it is preferable to increase the calcium ion concentration of the phosphoric acid-containing wastewater after adjusting the pH of the phosphoric acid-containing wastewater. Thereby, in the phosphoric acid containing waste water in an electrolytic cell, it becomes possible to make calcium carbonate hardly precipitate, fully increasing the supersaturation degree of calcium hydroxyapatite.
Further, since precipitation of calcium carbonate hardly occurs in the electrolytic cell, sludge and scale are hardly generated.

If the calcium ion concentration of the phosphoric acid-containing wastewater is adjusted first, calcium carbonate is likely to precipitate in the electrolytic cell, and the electrolytic cell may be contaminated. However, when the pH of the phosphoric acid-containing wastewater is 6 or less, or when the amount of calcium ions added to the phosphoric acid-containing wastewater is small, before adjusting the pH of the phosphoric acid-containing wastewater, Even when the calcium ion concentration is increased, calcium carbonate is hardly precipitated.

  Next, in the reaction crystallization tank 39, calcium ions are supplied, and calcium hydroxyapatite is crystallized from the phosphoric acid-containing wastewater in which the calcium hydroxyapatite is supersaturated.

  Moreover, in this embodiment, it is preferable to provide a crystal drawing means for separating and collecting calcium hydroxyapatite produced by the crystallization reaction in the reaction crystallization tank 39.

  Moreover, the calcium ion concentration already contained in phosphoric acid containing waste water may be high. In such a case, when the pH of the phosphoric acid-containing wastewater is adjusted to 8 to 9 in the electrolytic bath 31, the supersaturation degree of calcium hydroxyapatite becomes high, aggregated nuclei are formed, and calcium hydroxyapatite precipitates. There is. For this reason, also in this embodiment, it is preferable to provide observation means that can observe the inside of the electrolytic cell. Any observation means may be used as long as the inside of the electrolytic cell can be observed. Moreover, you may enable it to confirm from the exterior whether precipitation was able to be formed in phosphoric acid containing waste water by comprising at least one part of an electrolytic vessel with transparent members, such as glass and an acrylic resin. Accordingly, it is possible to increase the energization power as much as possible within a range where precipitation does not precipitate while confirming whether precipitation of calcium hydroxyapatite does not occur.

  When the concentration of calcium ions already contained in the phosphoric acid-containing wastewater is high, by increasing the pH of the phosphoric acid-containing wastewater as much as possible in the electrolytic cell, it avoids phosphate aggregation in the electrolytic cell and has a higher degree of supersaturation. That is, the phosphoric acid-containing wastewater can be led to the reaction crystallization tank in a state where crystallization is easier. In this case, since the aggregation reaction of calcium hydroxyapatite may occur, it is better not to add a solution containing calcium ions to the phosphoric acid-containing wastewater discharged from the electrolytic cell.

When the variation in the concentration of the phosphorus component contained in the phosphoric acid-containing wastewater is small, as in the first embodiment, once the electric power of the energizing means is controlled and the pH of the phosphoric acid-containing wastewater is adjusted, long-term over,必short not to adjust the power of the energization means. Thereby, it becomes possible to process phosphoric acid containing waste water, passing water continuously through an electrolytic cell.
In the case where the concentration of the phosphorus component in the phosphoric acid-containing wastewater varies greatly, the power for energization is adjusted again when precipitation occurs in the phosphoric acid-containing wastewater.

  Moreover, it is preferable that the phosphorus removal apparatus of this embodiment has a pH measurement means for measuring the pH of the phosphoric acid-containing wastewater in the electrolytic cell. Thereby, it becomes possible to adjust the pH of the phosphoric acid containing waste water in an electrolytic cell so that it may become a predetermined value or a predetermined range. The pH of the phosphoric acid-containing wastewater can be adjusted by adjusting the power for energization between the anode and the cathode by the energizing means. The adjustment of the power by the energization means may be automatically performed by the pH control means for controlling the energization means based on the measurement result from the pH measurement means, or may be performed manually. At this time, the pH of the phosphoric acid-containing wastewater is preferably 8.5 or more.

  Thus, it is necessary to change the calcium ion concentration of the solution containing calcium ions to be added to the phosphoric acid-containing wastewater later by adjusting the pH of the phosphoric acid-containing wastewater so as to be a predetermined value or a predetermined range. Almost disappears. Thereby, formation of the supersaturated state of calcium hydroxyapatite can be performed stably.

  The measurement and control of the pH of the phosphoric acid-containing wastewater may be about once a day. When the water quality of the phosphoric acid-containing wastewater is stable, the phosphorus component removal process can be stably performed even at a measurement interval such as once a month to once a year.

  The pH of the phosphoric acid-containing wastewater can be measured by introducing a pH sensor in-line into the phosphoric acid-containing wastewater.

As shown in FIG. 11, in the phosphorus removal apparatus of this embodiment, as in the fifth embodiment, at least a part of the waste water discharged from the reaction crystallization tank 39 is energized in the electrolytic tank 31 to adjust the pH. It is preferable to provide a circulation means 92 that merges and mixes with the phosphoric acid-containing wastewater after adjustment. In FIG. 11, the same components as those in FIG. 9 are given the same numbers.
Thereby, it becomes possible to increase the chance that the calcium hydroxyapatite constituent component in the waste water discharged from the reaction crystallization tank comes into contact with the seed crystal in the same manner as described above.

  In the phosphorus removal apparatus shown in FIG. 11, at least part of the waste water discharged from the reaction crystallization tank is discharged from the electrolytic tank, and the phosphoric acid-containing waste water after the addition of the aqueous solution containing calcium ions is added. Have been joined. At least a part of the waste water discharged from the reaction crystallization tank may be mixed with the phosphoric acid-containing waste water before the aqueous solution containing calcium ions is added to the phosphoric acid-containing waste water discharged from the electrolytic tank.

Embodiment 8
FIG. 12 shows a phosphorus removal apparatus according to still another embodiment of the present invention.
The phosphorus removal apparatus 100 in FIG. 12 includes an electrolytic cell 101 in which phosphoric acid-containing wastewater is accommodated and two electrode groups. Each electrode group includes a flat anode 102, a flat cathode 103, and a diaphragm 104 sandwiched between them. The two electrode groups are arranged in the electrolytic cell 101 so that the cathode 103 faces the electrode group. Moreover, the seed crystal 105 is added to the electrolytic bath, and the electrolytic bath also functions as a reaction crystallization bath. As the diaphragm 104, a cation exchange membrane is used as described above.

  In the phosphorus removal apparatus of FIG. 12, the electrolytic cell 101 has a shape in which a conical lower part, a cylindrical body, and an upper part extending outward in a tapered shape are combined. The two electrode groups are arranged so as to come to the upper part spreading outward in a tapered shape.

  The phosphorus removing apparatus in FIG. 12 further includes a stirring means 106 using a blower, a cylindrical draft tube 107 for forming a circulation path in the electrolytic cell, and a calcium ion supply means 108. The calcium ion supply means 108 includes a tank 108a that stores an aqueous solution containing calcium ions, and a pump 108b that transfers the aqueous solution to an electrolytic cell. Further, a supply unit having another configuration can be used.

In the phosphorus removal apparatus shown in FIG. 12, phosphoric acid-containing wastewater is introduced into the electrolytic cell from the conical lower portion by a pump 109 at a predetermined speed. At this time, when the concentration of calcium ions contained in the phosphoric acid-containing wastewater is less than 20 mg / L, the calcium ion concentration contained in the phosphoric acid-containing wastewater is set to 20 mg / L to 100 mg / L using calcium ion supply means. L is preferable.
In addition, you may use means other than the said pump for the introduction | transduction to the electrolytic cell of phosphoric acid containing waste_water | drain.

  Next, electricity is applied between the anode 102 and the cathode 103 using an energizing means (not shown). By energization, the phosphoric acid-containing wastewater is electrolyzed, and hydroxide ions are generated from the cathode. The produced hydroxide ions are supplied to the phosphoric acid-containing waste water between the two electrode groups, and a supersaturated state of calcium hydroxyapatite is formed.

A seed crystal is movably accommodated in the electrolytic cell. The seed crystal is moved upward in the draft tube 107 by the stirring means 106 made of a blower so that the seed crystal moves between the two cathodes, that is, in contact with the supersaturated phosphoric acid-containing waste water. Let Then, as described above, calcium hydroxyapatite that was in a supersaturated state is precipitated on the surface of the seed crystal.
Thereafter, the seed crystal on which calcium hydroxyapatite is deposited passes through the outside of the draft tube and moves to the conical lower portion. In FIG. 12, the enlarged seed crystal 110 exists in the conical lower part. These enlarged seed crystals are preferably periodically removed from the electrolytic cell by, for example, a crystal drawing means (not shown).

  The waste water after removing the phosphoric acid component overflows from the upper part spreading outward in a taper shape and is discharged to the outside. At this time, the electrode group on the left side of FIG. 12 functions as a solid-liquid separation means so that the seed crystals and SS components contained in the phosphoric acid-containing wastewater in the electrolytic cell do not move to the discharge port to the outside. is doing.

Next, an example of actually operating the phosphorus removal apparatus of the present embodiment will be shown.
An electrolytic cell having a volume of about 5 L was used. Moreover, a seed crystal made of calcium hydroxyapatite was put in the electrolytic cell. A seed crystal having an average particle diameter of 0.2 mm was used.

Phosphoric acid-containing wastewater having a soluble phosphorus concentration (SP) (that is, phosphoric acid concentration) of 4 ppm and a calcium ion concentration of 40 ppm out of 5 ppm of total phosphorus concentration (TP) is removed of phosphorus as shown in FIG. Water was passed through the apparatus at a rate of SV2 (1 / h). From the lower part of the electrolytic cell, aeration was performed at 1 L / min with a stirring means to form a circulating flow inside the electrolytic cell. Here, SV2 is a water flow rate such that the residence time is 30 minutes.
A voltage of 20 V was applied between the anode and the cathode to electrolyze the phosphoric acid-containing waste water. The phosphorus concentration in the phosphoric acid-containing wastewater near the cathode was measured over time. After 1 hour, the value of the phosphoric acid concentration decreased, and after 1 hour, the value became stable and became 1.5 ppm. At this time, the pH of the phosphoric acid-containing wastewater in the electrolytic cell was 8.8.
In the above example, since the calcium concentration in the phosphoric acid-containing wastewater was 40 ppm, calcium ions were not supplied.

Embodiment 9
FIG. 13 shows a phosphorus removal apparatus according to still another embodiment of the present invention. In FIG. 13, the same components as those in FIG.
The phosphorus removal apparatus 200 in FIG. 13 includes one cylindrical electrode group instead of the two electrode groups in FIG. As shown in FIG. 14, the electrode group includes a cylindrical diaphragm 202, a cylindrical cathode 203 disposed inside the diaphragm 202, and a cylindrical anode 201 disposed outside the diaphragm 202. As the diaphragm, a cation exchange membrane is used as described above.
Furthermore, two flat dam plates 206 are provided on the taper-shaped upper portion of the electrolytic cell. In this embodiment, both the weir plates in FIG. 13 function as solid-liquid separation means.

  As in the eighth embodiment, phosphoric acid-containing wastewater is introduced into the electrolytic cell from the conical lower portion by a pump 109 at a predetermined rate. Also in this embodiment, when the concentration of calcium ions contained in the phosphoric acid-containing wastewater is less than 20 mg / L, the calcium ion concentration contained in the phosphoric acid-containing wastewater is set to 20 mg using the calcium ion supply means. / L to 100 mg / L is preferable.

Next, electricity is applied between the anode 201 and the cathode 203 using an electricity supply means (not shown). By energization, the phosphoric acid-containing wastewater is electrolyzed, and hydroxide ions are generated from the cathode. The produced hydroxide ions are supplied at least to the phosphoric acid-containing waste water in the cathode chamber 204 inside the cylindrical cathode, and a supersaturated state of calcium hydroxyapatite is formed. The seed crystal is moved upward in the cathode chamber 204 by the stirring means 106 made of a blower. Then, as described above, calcium hydroxyapatite that was in a supersaturated state is precipitated on the surface of the seed crystal.
Then, seed crystals of calcium hydroxyapatite deposited on its surface passes through the outer side of the electrode group is moved to the bottom of the cone shape. As shown in FIG. 13, an enlarged seed crystal 110 exists in the conical lower portion. These enlarged seed crystals are preferably periodically extracted from the electrolytic cell by a crystal drawing means (not shown) in the same manner as described above.

  The phosphoric acid-containing waste water after the removal of the phosphoric acid component overflows from the upper part spreading outward in a taper shape and is discharged to the outside.

  In the present embodiment, 0.1 wt% saline is passed through the anode chamber 205 in which the anode is disposed. Since hydrogen ions are generated from the anode by electrolysis, the pH of the saline solution in the anode chamber becomes acidic. By adding this acidic water to the waste water after the phosphoric acid component is removed and discharged from the electrolytic cell, the waste water after discharged from the electrolytic cell can be neutralized. The acidic water can be added to the waste water by, for example, the acidic water transfer means 207. The acidic water transfer means can be composed of, for example, a pump.

Next, an example of actually operating the phosphorus removal apparatus of the present embodiment will be shown.
An electrolytic cell having a volume of about 5 L was used. Moreover, a seed crystal made of calcium hydroxyapatite was put in the electrolytic cell. A seed crystal having an average particle diameter of 0.2 mm was used.

Phosphoric acid-containing wastewater having a soluble phosphorus concentration (SP) (that is, phosphoric acid concentration) of 3.5 ppm and a calcium ion concentration of 40 ppm out of 4 ppm of total phosphorus concentration (TP) is obtained as shown in FIG. Water was passed through the removal device at a speed of SV2 (1 / h). Aeration was performed at 1 L / min from the lower part of the electrolytic cell with a stirring means to form a circulating flow inside the electrolytic cell.
A voltage of 20 V was applied between the anode and the cathode to electrolyze the phosphoric acid-containing waste water. The phosphorus concentration in the phosphoric acid-containing wastewater near the cathode was measured over time. After 1 hour, the value of the phosphoric acid concentration decreased, and after 1 hour, the value became stable and became 0.8 ppm. At this time, the pH of the phosphoric acid-containing wastewater in the electrolytic cell was 10.4.
In addition, also in the said example, since the calcium concentration in phosphoric acid containing waste water was 40 ppm, supply of calcium ion was not performed.

  In the eighth embodiment and the ninth embodiment, an example in which a blower is used as the stirring means has been described. As the stirring means, a stirring blade as described in the first embodiment may be used. Further, the eighth embodiment and the ninth embodiment may be used in combination with other embodiments.

  In the present invention, the first embodiment may be used in combination with other embodiments, or the first embodiment may be combined with all of the second to seventh embodiments.

  INDUSTRIAL APPLICABILITY According to the present invention, it is possible to provide a phosphorus removal apparatus that removes phosphate ions in water with high efficiency. Furthermore, the phosphorus removing apparatus of the present invention can make the waste water contained in the cathode chamber alkaline by electrolysis. For this reason, for example, it is also useful as an apparatus for a water purification method or the like that removes heavy metal ions, boron, and the like contained in waste water from water as insoluble hydroxides. Further, by changing the components contained in the solution in the anode chamber and the components contained in the solution in the cathode chamber, it can be used for applications such as producing chemicals and pharmaceuticals by reaction crystallization.

It is the schematic which shows the waste water treatment facility provided with the removal apparatus of phosphorus of this invention. It is the schematic which shows the wastewater treatment facility of another form provided with the phosphorus removal apparatus of this invention. It is the schematic which shows the phosphorus removal apparatus concerning one Embodiment of this invention. It is the schematic which shows the phosphorus removal apparatus concerning another embodiment of this invention. It is the schematic which shows the phosphorus removal apparatus concerning another embodiment of this invention. It is the schematic which shows the phosphorus removal apparatus concerning another embodiment of this invention. It is the schematic which shows the phosphorus removal apparatus concerning another embodiment of this invention. It is the schematic which shows the phosphorus removal apparatus concerning another embodiment of this invention. It is the schematic of the phosphorus removal apparatus concerning another embodiment of this invention. Shows the solubility curve of the calcium carbonate cases have small and if alkalinity is large. It is the schematic of the phosphorus removal apparatus concerning another embodiment of this invention. It is the schematic which shows the phosphorus removal apparatus concerning another embodiment of this invention. It is the schematic which shows the phosphorus removal apparatus concerning another embodiment of this invention. It is a cross-sectional view which shows roughly the electrolytic cell used for the phosphorus removal apparatus shown by FIG.

Explanation of symbols

10, 20 Wastewater treatment facility 11 First sedimentation tank 12 Biological treatment layer 13 Second sedimentation tank 14 Sludge treatment tank 15, 30, 40, 50, 60, 70, 80, 90, 100, 200 Phosphorus removal device 16 Return means 17 Sludge treated water transfer means 21 Sludge solubilization tank 22 Solid separation tank

31, 101 Electrolyzer 32 Anode chamber 33 Cathode chamber 34, 104 Diaphragm 35, 102 Anode 36, 103 Cathode 37, 106 Agitation means 38 Current supply means 39 Reaction crystallization tank 41 Measuring means 51 Storage tank 52 Pump 61 Neutralization tank 62 Transfer Means 71, 92 Circulation means 81, 105 Seed crystals 91, 108 Calcium ion supply means 107 Draft tube 108a Tank 108b, 109 Pump 110 Enlarged crystal 201 Cylindrical anode 202 Cylindrical diaphragm 203 Cylindrical cathode 204 Cathode chamber 205 Anode chamber 206 Dam plate 207 Acidic water transfer means

Claims (15)

(1) An electrolytic cell comprising an anode and a cathode and containing at least phosphoric acid-containing waste water,
(2) Energizing means to energization between the anode and the cathode,
(3) Calcium ion supply means for supplying calcium ions to the phosphoric acid-containing wastewater, and (4) a solid that separates the phosphorus-containing crystals precipitated from the phosphoric acid-containing wastewater and the wastewater after the phosphorus-containing crystals are precipitated. Comprising liquid separating means ,
The electrolytic cell includes the anode, an anode chamber into which an aqueous solution containing calcium ions is introduced; a cathode chamber that includes the cathode and into which phosphoric acid-containing wastewater is introduced; and between the cathode chamber and the anode chamber. A separator for removing phosphorus, which supplies calcium ions to the phosphoric acid-containing waste water by energizing between the anode and the cathode . Further comprising Claim 1 phosphorus removal apparatus according to means for supplying an aqueous solution containing calcium ions to the means and said anode chamber for introducing a phosphate-containing waste water into the cathode chamber. Apparatus for removing phosphorus as claimed in claim 1, further comprising a calcium ion concentration adjusting means for adjusting the calcium ion concentration of the aqueous solution containing the calcium ion. Wherein the generated anode water in the anode chamber, the phosphorus removal device phosphorus-containing crystal comprises neutralizing means for neutralizing by adding to the waste water after separating claim 1. The phosphorus removal apparatus according to claim 4 , further comprising a biological treatment tank for biologically treating the wastewater after being neutralized by the neutralizing means. (1) An electrolytic cell comprising an anode and a cathode and containing at least phosphoric acid-containing waste water,
(2) energization means for energizing between the anode and the cathode;
(3) Calcium ion supply means for supplying calcium ions to the phosphoric acid-containing waste water, and
(4) Solid-liquid separation means for separating phosphorus-containing crystals deposited from the phosphoric acid-containing wastewater and wastewater after the phosphorus-containing crystals are deposited
Comprising
Said electrolytic cell, the anode, the cathode, and at least one organic group of electrodes consisting of arranged diaphragm between the anode and the cathode,
In one of the at least one electrode group, the diaphragm is cylindrical, the cylindrical cathode is disposed inside the cylindrical diaphragm, and the cylindrical cathode is disposed outside the cylindrical diaphragm. A phosphorus removal device in which the anode is arranged. The phosphorus removing apparatus according to claim 6 , wherein the seed crystal is movably held in the electrolytic cell. The phosphorus removal apparatus according to claim 6, wherein at least one of the electrode groups functions as the solid-liquid separation unit. The phosphorus removal apparatus according to any one of claims 1 to 8, further comprising supply means for supplying the phosphoric acid-containing wastewater to the electrolytic cell. The phosphorus removal apparatus in any one of Claims 1-9 which supplies a calcium ion to the phosphoric acid containing waste water after the said calcium ion supply means is discharged | emitted from the said electrolytic vessel. The phosphorus removal apparatus according to any one of claims 1 to 10, wherein the solid-liquid separation means holds seed crystals. The phosphorus removing apparatus according to any one of claims 1 to 11, further comprising a crystal drawing means for discharging the phosphorus-containing crystal. The phosphorus removal apparatus according to any one of claims 1 to 12, further comprising measuring means for measuring at least one of a hydrogen ion concentration (pH), a calcium ion concentration, and a phosphoric acid concentration in the phosphoric acid-containing waste water. The phosphorus of any one of Claims 1-13 further provided with the circulation means for making at least one part of the waste_water | drain discharged | emitted from the said solid-liquid separation means join the phosphoric acid containing waste_water | drain discharged | emitted from the said electrolytic vessel. Removal device. (1) An electrolytic cell comprising an anode and a cathode and containing at least phosphoric acid-containing waste water,
(2) Energizing means to energization between the anode and the cathode,
(3) Calcium ion supply means for supplying calcium ions to the phosphoric acid-containing wastewater, and (4) a solid that separates the phosphorus-containing crystals precipitated from the phosphoric acid-containing wastewater and the wastewater after the phosphorus-containing crystals are precipitated. A method for operating a phosphorus removal apparatus comprising a liquid separation means,
An operation method in which the pH of the phosphoric acid-containing waste water is adjusted to 8.5 to 10 and the calcium ion concentration is adjusted to 20 mg / L to 100 mg / L by using at least one of the energization means and the calcium supply means.

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